Equine myenteric ganglionitis: a case of chronic intestinal pseudo-obstruction.

A 4-year-old Standardbred mare was referred to the New York State College of Veterinary Medicine for colic evaluation. Physical examination revealed a small colon impaction which initially responded to conservative medical management. Her signs soon recurred, however, and an exploratory celiotomy was recommended. At surgery the small colon impaction was confirmed. The impaction was evacuated and a surgical biopsy was submitted for histopathologic evaluation. Microscopic examination of H&E and Trichrome sections revealed a massive mononuclear cell infiltration of the myenteric plexus. In addition, there was remarkable fibrosis within the neuropil of the myenteric ganglia and interganglionic fascicles. Postoperatively, the mares's colic signs recurred within two weeks and she was euthanatized. Samples of the proximal and distal small colon as well as the original biopsy site were obtained. Over the intervening two weeks, the inflammatory infiltrate within the myenteric ganglia had subsided, while the previous intraganglionic and fascicular fibrosis had increased substantially. The number of myenteric neurons appeared diminished when compared to age-matched controls. There was evidence of neuronal degeneration among the surviving neurons including central chromatolysis and cytoplasmic vacuolization. Furthermore, many degenerate axons were observed with the electron microscope. This scenario represents an equine example of chronic idiopathic intestinal pseudo-obstruction (CIIP) which has been extensively described in the human literature. In this case, the syndrome arose as a consequence of recurrent inflammatory injury to the mare's enteric nervous system, thereby altering normal gastrointestinal motility. The ensuing neurogenic functional obstruction manifested as frequent bouts of small colon impactions. Equine CIIP should be considered in the differential diagnosis of colic.